Cyclobutadienes via an Organocascade

Key words

cyclobutadienes - ynals - α,β-unsaturated aldehydes - [2+2] cycloaddition

Significance

The Wang group reports an organocatalytic [2+2] cycloaddition between α,β-unsaturated aldehydes and ynals. This reaction is catalyzed by secondary amines and generates cyclo-butadienes in high yields under mild conditions.

Comment

The authors suggest that the reaction follows a dienamine–iminium–allenamine cascade sequence furnishing cyclobutadienes as products. Typically high temperatures are required for the synthesis of cyclobutadienes. This method requires only room temperature, hence overcoming a limitation of previous methods.